1. Field of the Invention
The invention relates to a three-dimensional image display system having a system axis which extends from a light-generating element to an observation window, said image display system being provided with at least two image display devices which are congruently aligned with each other and placed at different positions along the system axis, and are provided with a control circuit.
2. Description of the Related Art
An image display device is herein understood to mean a device for converting an electric image signal presented to the control circuit of this device into a visible image. Such a device may be constituted by, for example, a cathode ray tube or by an image display panel which is provided with a layer of liquid crystalline material and whose operation is based on a change of the state of polarization of light incident thereon, or an image display panel which is provided with a polymer layer in which cells of liquid crystalline material are dispersed and whose operation is based on light scattering. Such panels are placed one behind the other on the system axis. When cathode ray tubes are used, these tubes may be placed, for example, in such a way that their face plates are situated in mutually perpendicular planes, and the images from these tubes can be combined with, for example, a partially transmissive mirror which is placed, for example, at an angle of 45.quadrature. to said planes. This mirror combines the (sub-)axes of the tubes to one system axis which extends as far as the observation window.
In a three-dimensional image display system with cathode ray tubes, these tubes are also light-generating elements. In a system with liquid crystalline image display panels, the light-generating element is a radiation source unit which illuminates the panels.
The observation window may be a physical window, i.e., a light-transmissive aperture in an envelope in which the various components of the image display system are accommodated, but also an imaginary window, i.e., a plane which marks the beginning of the audience space and in which the image is formed.
The fact that the image display devices are aligned congruently with respect to each other means that not only the centers of the images formed by these image display devices are coaxial, but also corresponding image components are in registry. The image surfaces themselves of the image display devices need not be mutually parallel in that case.
There is a great need of three-dimensional image display systems, particularly in medical diagnostic techniques, notably, when analyzing and visually representing image information obtained by means of X-ray tomography or a magnetic resonance technique, but also in diagnostic systems using sound waves, positron emission tomography, ECT (Emission Computed Tomography) or MMI (MultiModal Imaging). Moreover, there is a need of three-dimensional image display systems for displaying computer-generated images, i.e., computer graphics. An effective three-dimensional image display system will not only be a breakthrough in these professional fields, but also in the field of consumer uses, notably for TV apparatus and multimedia systems. Such a system should be user-friendly, i.e., it should be able to work without the viewer needing auxiliary means, such as polarizing spectacles, and it should be suitable for a plurality of users watching at the same time and thus have, for example, a large viewing angle.
A three-dimensional image display system of the type described in the opening paragraph is known from, for example, U.S. Pat. No. 5,113,272. The system described in this patent comprises at least two, but preferably a much larger number of image display panels which are preferably based on light scattering. The three-dimensional effect must be obtained by displaying, with the given number of panels, an equally large number of images of object cross-sections in planes perpendicular to the system axis so that, when viewed from the viewer, the successive images cover, for example an increasingly larger or smaller surface area of the associated panels. This is dependent on whether the object to be displayed becomes wider or narrower in said direction. The three-dimensional effect is based on parallax simulation and, to obtain a sufficiently strong effect, the different, scattering or liquid crystalline layers should be placed at sufficiently large distances from each other. Moreover, there should be a sufficiently large number of these layers, up to twenty, so that only a small part of the illumination beam intensity can reach the viewer.